This invention relates to electromagnetically actuable devices and, more particularly, to an electromagnet incorporating a shading coil.
A typical electromagnetically actuable device has a magnetic core proximate an armature. A coil is selectively energized to draw the armature to the magnetic core. The device may be a solenoid, a contactor, a motor starter, or the like. The armature is operatively associated with a movable device such as movable contacts or an actuator. In many instances the coil is selectively energized from an AC power source. With AC-operated electromagnets, elimination or control of noise is a prime concern. To minimize noise the surface interface of the magnetic core and armature of each device must be matched to provide minimal magnetic xe2x80x9cair gapxe2x80x9d and a stable interface surface. The minimal air gap assures sufficient force to prevent movement and the stable surface interface prevents movements due to the widely changing forces in the AC-operated device. Particularly, a spring provides a constant force between the magnetic core and the armature. Energization of the coil counteracts the spring force to draw the armature toward the magnetic core. However, with an AC power source operating at, for example, 60 Hz, there are 120 zero crossings each second during energization. At each zero crossing the spring force may overcome the magnetic force causing the armature to be pushed away and then drawn back again. This can produce a noisy electromagnet.
Conventional shading coils have been used without success to address this problem. A conventional shading coil drives the formation of a small shaded magnetic pole formed on the interface or mating surface of the core or armature. The conventional shading coil is typically a conductive alloy in a stamped ring that is attached to the laminations of the AC electromagnet. These conventional coils routinely break and therefore are costly to produce and assemble. Also, the laminations of conventional coils are often held together with rivets that add costs to producing the electromagnets. The rivets provide points of failure. Accordingly, the inherent weakness of the rivets and the conventional shading coils typically limit the mechanical life of the electromagnet.
In accordance with the invention, a shading coil is formed in an electromagnet by welding or brazing or the like.
Broadly, there is disclosed herein an electromagnetically actuable device having a magnetic core proximate an armature and a coil selectively energized to draw the armature to the magnetic core. The device comprises the armature and magnetic core being of laminated magnetic steel and having mating surfaces. At least one of the armature and magnetic core includes means for integrally securing laminations together to define a conductive path proximate the mating surface to provide a shading coil.
It is a feature of the invention that the securing means comprises weld connections between adjacent laminations of the at least one of the armature and magnetic core.
It is another feature of the invention that the securing means comprises braze connections between adjacent laminations of the at least one of the armature and magnetic core. The braze connections may use a conductive alloy such as copper.
It is still another feature of the invention that the securing means comprises the sole means for securing the laminations together.
It is a further feature of the invention that a single conductive line is provided on the mating surface transverse to the laminations and a plurality of conductive lines are provided below the mating surface transverse to the laminations. It is a further feature of the invention that the single conductive line is of greater depth than the plurality of conductive lines.
There is disclosed in accordance with another aspect of the invention an electromagnetically actuable device having a magnetic core proximate an armature and a coil selectively energized to draw the armature to the magnetic core. The device comprises the armature and magnetic core including laminations of magnetic steel and having mating surfaces and at least one of the armature and one of the magnetic core including conductive areas formed integrally with the laminations to define a conductive path proximate the mating surface to provide a shading coil.
There is disclosed in accordance with still another aspect of the invention the method of forming an electromagnet having a magnetic core and an armature. The method comprises providing an armature and magnetic core formed of lamination of magnetic steel and having a mating surface and integrally securing the laminations together to define a conductive path proximate the mating surface to provide a shading coil.
Further features and advantages of the invention will be readily apparent from the specification and from the drawings.